Combined gas and steam power cycle



July 16, 1963 R. c. ROE 3,09

COMBINED GAS AND STEAM POWER CYCLE Filed Feb. 9, 1961 G's/surname HIECOMPEESSOE INVHVTOR. PAL PH C Pas.

BY MMMW-W ATTORNEK).

United States Patent 3,097,486 COMBINED GAS AND STEAM POWER CYCLE RalphC. Roe, Tenatly, N.J., assignor to Burns and Roe, Inc, New York, N.Y., acorporation of New Jersey Fiied Feb. 9, 1961, Ser. No. 88,037 2 Ciaims.(Cl. ell-49.18)

This invention relates to power plants, and more particularly, to suchplants comprising a combined gas and steam cycle for power generation.

Recent technological advances have made it practical to combine gasturbine cycles with steam cycles, such combined systems providingcertain advantages including increased station output for the same steamflow by virtue of the fact that the gas turbine produces power as wellas the steam turbine and, further, the overall station efficiency isimproved by the combined cycle and a reduction is thereby achieved inthe total cost per net kilowatt-hour as compared to the conventionalsteam-turbine cycle.

Those persons skilled in the art will readily appreciate that gasturbine systems involving combustion of fuel in the turbines to drivesame have the disadvantage that the hot dust laden combustion gaseserode, corrode and destroy the various turbine parts. Additionally,these sys tems have only a narrow application since the fuel must be asacceptable as possible to the turbine. Accordingly, it has been proposedto provide hot air turbine systems in which air is compressed and heatedout of contact with products of combustion and then delivered to a gasturbine for driving same so that any fuel can be used in the furnace. Insuch systems, a small portion of the turbine exhaust has been utilizedto support combustion of fuel used to heat the air. However, in systemsof this type, problems have arisen concerning control of the rate ofcombustion and consequent heating of the compressed air as the powerdemand on the turbine varies. Additionally, the problem of maintainingthe air heater at a reasonable temperature to assure its structuralintegrity has caused considerable difliculty.

I have contributed by my invention, a novel combined gas and steam powercycle which eliminates the foregoing problems through a constructionthat is emcient and yet relatively simple. The present concept is basedupon an awareness that a relatively great amount of fuel is burned togenerate steam thus requiring a great amount of combustion supportingair, and that boiler output is desirably a function of the power demandon the system.

In essence, my combined cycle has a steam generator or boiler includinga furnace, a steam operated turbine connected to receive steam from thegenerator, an air heater disposed in heat transfer relation to the samefurnace, compressor means supplying air under pressure to the heater,and gas operated turbine means connected to receive heated compressedair from the heater.

As a particular feature of my invention, I provide means for deliveringthe entire exhaust from the gas turbine to the furnace to support thecombustion of fuel therein, this exhaust constituting the sole supply ofcombustion air for the furnace. This feature of the invention, incombination with speed or air flow control means sensing the powerdemands on the plant and regulating the compressor output, and thus theturbine speed or air control accordingly, effectively controls the rateof fuel combustion in the furnace. Thus, it will be appreciated that thehigher the demands on the system, the hotter the furnace automaticallywill be, and conversely, the lower the demands on the system, thesmaller the rate of flow of air that will pass through the turbine andto the furnace to support combustion, thereby reducing the heat output.In accordance with this feature of the invention, a minimum of excessair is utilized for combustion thus assuring the most efficientconversion of fuel "ice into heat energy and the maintenance of maximumfurnace temperatures for a given quantity of fuel consumed.

As has already been stated, the air heater is disposed in heat transferrelation to the furnace. Actually, the air heater may comprise a unithaving a large surface area positioned in the radiant heat section ofthe steam generator. Thus, as the load demand on the system varies, andthe compressor output is regulated by the speed control or air controlmeans, the rate of flow of air through the air heater is also regulated,wherefore as the furnace becomes hotter, a greater quantity of air isautomatically passed through the radiant air heater to maintain thisunit cool enough to assure structural integrity.

As another feature of my invention, means are provided for tapping aportion of the compressed air before it enters the heater, and thistapped air is introduced into the heater at a zone intermediate itsinlet and outlet. In this way, the temperature of the air leaving theheater may be controlled. Damper means may be provided in the bypass toregulate the flow of air bypassing the initial portion of the heater. Insome instances, it may be desirable to bypass a portion of thecompressed air around the heater altogether and deliver the same to theinlet side of the gas turbine along with the heated air.

There has thus been outlined rather broadly the more important featuresof the invention in order that the detailed description thereof thatfollows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described hereinafterand which will form the subject of the claims appended hereto. Thoseskilled in the art will appreciate that the conception upon which thisdisclosure is based may readily be utilized as a basis for the designingof other structures for carrying out the several purposes of theinvention. It is important, therefore, that the claims be regarded asincluding such equivalent constructions as do not depart from the spiritand scope of the invention.

A specific embodiment of the invention has been chosen for purposes ofillustration and description and is shown in the accompanying drawing,forming a part of the specification, wherein the single FIGURE is adiagrammatic illustration of a combined system according to the presentinvention.

Referring now to the drawing, there is shown a steam generator or boiler10 including a furnace 11 of conventional construction. Steam isdelivered through a steam line 12. from the generator '10 to the inputside :of a steam turbo-generator 14, for example, to drive same.

The combined system of the present invention also includes an aircompressor 15 which compresses atmospheric air and delivers it through aline 16 to an air heater 17 positioned in the steam generator 10. Theheater illustrated includes a divided header 19, land the compressed airis admitted to the heater through its upper or inlet side, as shown. Theheated compressed air is discharged from the heater through the otherside of the header and is delivered through line 20 to a gas driventurbine-generator 21, for example, which utilize-s part of its output todrive the compressor 15. As shown in the drawing, a line 22 conducts thetotal air exhaust from the turbine-generator 21 to the furnace 11 wherethis air constitutes the entire supply of air utilized to supportcombustion.

Actually, the air heater 17 comprises in its preferred form, a series ofsteel tubes which are positioned in the radiant heat section of thesteam generator. The tubes may be provided in two sections, the firstconnecting the inlet side of the header 19 with a secondary header 24,and the second section connecting the secondary header with the outletside of the header 19. Thus, the compressed air passes through the firstsection of heater tubes thence through the secondary header to thesecond section, and finally to the outlet side of the header 19.

In order to maintain the operating temperature of the air driving thegas turbine 21 constant at all loads, I provide a bypass line 25 whichis tapped into compressed air line 16 and connects with the secondaryheader 24-, as shown. This bypass line 25 is equipped with a damper 26which may be controlled by a regulator (not shown) of conventionaldesign and responsive to temperature variations in the air leaving theheater 17. The line 25 may, if desired, bypass the heater 17 altogetherand connect directly to the line 20, for some applications. In any case,it is important to understand that the bypass is elfective to feedcooler air to the air in line 20 at rates to maintain the airtemperature constant to the turbine 21 at all load conditions.

In operation, the steam generator makes steam in the usual way fordelivery through steam line 12 to the steam turbo-generator 14. At thesame time, the compressor '15 compresses atmospheric air which isconducted through compressed air line 16 to the header 19 and theradiant airheater 17. The air, thus compressed and heated is conveyedvia line 20 to the gas turbine 21 for its operation. While expandingthrough the turbine, the air of course gives up a considerable portionof its heat, but upon being exhausted from the turbine will have atemperature of several hundred degrees Fahrenheit, and approximately 900F., in a typical case. All of this exhaust air is conveyed through line22 to the furnace 11 where it is admitted as the sole supply ofcombustion air.

It will be appreciated by those skilled in the art that the heat inputand hence the temperature in the furnace will be controlled by the usualcombustion control 30, which may be of the Bailey meter type, forexample which includes the usual steam tap 31, and steam and airorifices 32 and 34, all connected to the control meter 35 whereby theair and fuel flow to the furnace are controlled. The combustion controlmay respond to steam pressure or to the demands for steam of the steamturbine as controlled by the steam turbine governor. Additionally, thefurnace will be called upon to supply the heat required to operate thegas turbine system by heating the :air from the gas turbine compressorto temperatures suitable for operation of the gas turbine. Accordingly,and because of the coordination of the system which is the subject of myinvention, as the power demand drops, the required air for combustion isdecreased and hence the compressor output is reduced, the flow of airthrough the air heater and to the gas turbine is thereby reduced and thegas turbine exhaust, or furnace combustion air, is also reduced. Sinceless combustion supporting air flows to the furnace, the furnace heatinput and temperature are reduced, but the requirement for heating theair for the gas turbine is similarly decreased, and therefore it ispossible to maintain the air temperature from the heater substantiallyconstant. Conversely, as more power is demanded, governor 27 opens itsthrottle to the steam turbine, the combustion control demands more air,which in turn, acting either through the governor or the air control ofthe compressor, supplies more air to the heater and to the gas turbineand thence will supply from the gas turbine exhaust more air to thefurnace. The boiler in turn will supply more steam to the steam turbine.In this way the air requirements for combustion are coordinated with theair flow through the compressor, the air flow and the heat input in theheater, and the output of the gas turbine, the exhaust of which suppliesthe total cornbustion air. Regardless of whether the load increases ordecreases, the furnace heat input and temperature will respond to theheat requirements of the air heater and all will react according to theload demands on the combined steam and gas turbine system while the fuelis burned with 4 maximum thermal efficiency by virtue of the utilizationin the furnace of a minimum of excess combustion air.

It is also important to realize that by reason of the presentcontribution, as the power demand is increased, and the furnacetemperature rises, the rate of flow of air through the air heater 17 isalso increased, thus maintaining the heater tubes sufiiciently cool toprevent their destruction.

As has already been stated, a bypass is provided between the compressedair line 16 and the secondary header 24 of the air heater. By thismeans, the temperature of air to the gas turbine is maintainedsubstantially constant at all load conditions. Actually, the mass flowof air through the heater is directly proportional to the total heatrelease in the furnace so that when the demands on the steam boilerdecrease, mass flow through the heater decreases and the heat release inthe furnace decreases. Conversely, when the demands on the steamgenerator increase, the mass flow on the heater increases and the totalheat release of the furnace increases. The result is that by thiseconomic combination, the heater is largely selfregulating but to takecare of any possible lack of precise regulation, the bypass regulatesthe mass flow through a portion of the heater in order to obtainextremely close regulation of temperature at a substantially constantlevel. As the temperature of the air leaving the heater changes, theflow of bypassed air is reduced or increased by damper 26.

From the foregoing description, it will be seen that I contribute by myinvention, a combined steam and gas power cycle with fool-proof furnacetemperature control means for both the steam and gas sides of the cycle,which control means are automatically responsive to the power demandsmade on the system. It will also be seen that the air is heated in aradiant air heater in the steam boiler, the heater being self-regulatingto' the extent that the rate of air flow through the heater increases athigher furnace temperatures during periods of high power demands,wherefore the heater tubes cannot overheat.

I believe that the construction and operation of my novel combined steamand gas power system will now be understood and that the advantages ofmy invention will be fully appreciated by those persons skilled in theart.

I now claim:

1. In a power plant of the class described, a combination gas and steamcycle comprising, a steam generator including a single furnace, a steamoperated turbine connected to receive steam from said generator, an airheater disposed in the radiant zone of said furnace, means supplying airunder pressure to said radiant heater, gas operated turbine meansconnected to receive heated compressed air from said heater, meansdelivering the entire exhaust from said gas turbine to said furnace tosupport combustion of fuel therein, said gas turbine exhaustconstituting the sole supply of combustion air in said furnace, andcontrol means sensing variations in the demand on said power plant andregulating the flow of air under pressure to said heater and thus alsoto said furnace to vary the thermal output of said heater and steamgenerator in direct relation to variations in power requirements, theair flow through said heater thus being at all times automaticallyproportional to the heat generated to maintain the integrity of saidheater.

2. In a power plant of the class described, a combination gas and steamcycle comprising, a steam generator including a single furnace, a steamoperated turbine connected to receive steam from said generator, an airheater disposed in the radiant zone of said furnace, means supplying airunder pressure to said radiant heater, gas operated turbine meansconnected to receive heated compressed air from said heater, meansdelivering the entire exhaust from said gas turbine to said furnace tosupport combustion of fuel therein, said gas turbine exhaustconstituting the sole supply of combustion air in said furnace, a bypassfor conducting a portion of the air under pressure to said heater at apoint intermediate its inlet and References Cited in the file of thispatent outlet sides, a damper in said "bypass controlling the flow ofcompressed air therethrough, and control means sens- UNITED STATESPATENTS ing variations in the demand on said power plant and regulatingthe flow of air under pressure to said heater 5 Eggs; g

and thus also to said furnace to vary the thermal output of said heaterand steam generator in direct relation to FOREIGN PATENTS variations inpower requirements, the air flow through said heater thus being at alltimes automatically proportional 487,433 Canada Oct. 21, 1952 to theheat generated to maintain the integrity of said 10 1,038,643 France May13, 1953 578,628 Great Britain July 5, 1946 heater.

2. IN A POWER PLANT OF THE CLASS DESCRIBED, A COMBINATION GAS AND STEAMCYCLE COMPRISING, A STREAM GENERATOR INCLUDING A SINGLE FURNACE, A STEAMOPERATED TURBINE CONNECTED TO RECEIVE STEAM FROM SAID GENERATOR, AN AIRHEATER DISPOSED IN THE RADIANT ZONE OF SAID FURNACE, MEANS SUPPLYING AIRUNDER PRESSURE TO SAID RADIANT HEATER, GAS OPERATED TURBINE MEANSCONNECTED TO RECEIVE HEATED COMPRESSED AIR FROM SAID HEATER, MEANSDELIVERING THE ENTIRE EXHAUST FROM SAID GAS TURBINE TO SAID FURNACE TOSUPPORT COMBUSTION OF FUEL THEREIN, SAID GAS TURBINE EXHAUSTCONSTITUTING THE SOLE SUPPLY OF COMBUSTION AIR IN SAID FURNACE A BYPASSFOR CONDUCTING A PORTION OF THE AIR UNDER PRESSURE TO SAID HEATER AT APOINT INTERMEDIATE ITS INLET AND